Your pinky is a finger. Get it strong and make it work.
EDIT TO ADD: I went and played a song where I have to do that progression and paid attention to how I do it (a rare thing for me). I cheat. I use my pinky to get the C#, but I move my middle finger over from the D string second fret to the A string second fret to get the B, which leaves the D string open. You can make a bit of a tangle of your fingers and put your pinky on the second fret of the D string if you really, really want to avoid playing a "wrong" chord in the progression. It wouldn't bother me, and I sure wouldn't put you into messed up D chord jail if you did it. And I guarantee you, unless you are auditioning for Julliard or Peabody, no one will notice and if they do notice they wouldn't care because it would mean that they do the same darned thing.
- Zurf